DESCRIPTION

The
strtod(),
strtof(),
and
strtold()
functions convert the initial portion of the string pointed to by
nptr
to
double,
float,
and
long double
representation, respectively.

The expected form of the (initial portion of the) string is
optional leading white space as recognized by
isspace(3),
an optional plus ('+') or minus sign ('-') and then either
(i) a decimal number, or (ii) a hexadecimal number,
or (iii) an infinity, or (iv) a NAN (not-a-number).

A
decimal number
consists of a nonempty sequence of decimal digits
possibly containing a radix character (decimal point, locale-dependent,
usually '.'), optionally followed by a decimal exponent.
A decimal exponent consists of an 'E' or 'e', followed by an
optional plus or minus sign, followed by a nonempty sequence of
decimal digits, and indicates multiplication by a power of 10.

A
hexadecimal number
consists of a "0x" or "0X" followed by a nonempty sequence of
hexadecimal digits possibly containing a radix character,
optionally followed by a binary exponent.
A binary exponent
consists of a 'P' or 'p', followed by an optional
plus or minus sign, followed by a nonempty sequence of
decimal digits, and indicates multiplication by a power of 2.
At least one of radix character and binary exponent must be present.

An
infinity
is either "INF" or "INFINITY", disregarding case.

A
NAN
is "NAN" (disregarding case) optionally followed by '(',
a sequence of characters, followed by ')'.
The character string specifies in an implementation-dependent
way the type of NAN.

RETURN VALUE

These functions return the converted value, if any.

If
endptr
is not NULL,
a pointer to the character after the last character used in the conversion
is stored in the location referenced by
endptr.

If no conversion is performed, zero is returned and the value of
nptr
is stored in the location referenced by
endptr.

If the correct value would cause overflow, plus or minus
HUGE_VAL
(HUGE_VALF,
HUGE_VALL)
is returned (according to the sign of the value), and
ERANGE
is stored in
errno.
If the correct value would cause underflow, zero is
returned and
ERANGE
is stored in
errno.

ERRORS

ERANGE

Overflow or underflow occurred.

CONFORMING TO

C89 describes
strtod(),
C99
describes the other two functions.

NOTES

Since
0 can legitimately be returned
on both success and failure, the calling program should set
errno
to 0 before the call,
and then determine if an error occurred by checking whether
errno
has a nonzero value after the call.

EXAMPLE

See the example on the
strtol(3)
manual page;
the use of the functions described in this manual page is similar.